Magnetically latched switch assembly

ABSTRACT

A magnetically latched switch assembly including a reed switch mounted on a baseplate adjacent a biasing magnet, whose field strength and orientation are sufficient to hold the reed switch actuated but insufficient to independently actuate the switch. A LATCH magnet and a RELEASE magnet are separately mounted on a pair of reciprocating key stems, the former with magnetic poles opposing, the latter with magnetic poles assisting, the field associated with the biasing magnet. Movement of the LATCH magnet into proximity with the biasing magnet concentrates the field associated with the latter in the switch, closing the switch, which is subsequently held actuated by the latter. Movement of the RELEASE magnet into proximity with the biasing magnet reduces the field associated with the latter in the switch, opening the switch.

United States Patent Pedersen 1 Feb. 1, 1972 54] MAGNETICALLY LATCHED SWITCH Primary ExaminerBemard Gilhcany EMBLY Assistant ExaminerR. N. Envall, .Ir. ASS AttorneyPatrick J. Schlesinger, Charles R. Lepchinsky, [72] Inventor: Egon A. Pedersen, Pleasanton, Calif. Warren P. Kujawa and Jay M. Cantor [73] Assignee: The Singer Company, New York, NY. [57] ABSTRACT [22] Flled: 1971 A magnetically latched switch assembly including a reed [Zl] Appl.No.: 120,570 switch mounted on a baseplate adjacent a biasing magnet, whose field strength and orientation are sufficient to hold the reed switch actuated but insufficient to independently actuate [52] U.S.Cl ..335/207 the Switch A LATCH magnet and a RELEASE magnet are [51] P 13/00 H011 3/12 separately mounted on a pair of reciprocating key stems, the [58] Field of Search ..335/205, 206, 207, 153 former with magnetic poles opposing the latter with magnetic poles assisting, the field associated with the biasing magnet. {56] References c Movement of the LATCH magnet into proximity with the biasing magnet concentrates the field associated with the UNITED STATES PATENTS latter in the switch, closing the switch, which is subsequently 3,260,819 7/1966 Scuitto et al. ..3 35/207 X held actuated by the latter. Movement of the RELEASE mag- 3,3l9,l28 5/1967 Nilssen ..335/ 153 X net into proximity with the biasing magnet reduces the field associated with the latter in the switch, opening the switch.

11 Claims, 7 Drawing Figures :slsaslaes PATENTED FEB 1 1972 IVENTOR.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to bistable switch assemblies of the latching type. In another aspect, the invention relates to magnetically operable switches, in particular, switches having contact elements whose configuration can be controlled by magnetic fields.

2. Description of the Prior Art Various and diverse arrangements have been proposed constructing'bistable switching assemblies of the latching type. Such assemblies ordinarily employ two manually operable key assemblies and a mechanical latching arrangement in association with a set of switch contacts. In operation, momentary actuation of one of the keys places the switch contacts in a first configuration, e.g., closed, while momentary actuation of the other one of the keys places the contacts in their alternate configuration, e.g., open. The mechanical latching components maintain the switch contacts in the configuration selected by the operator until a subsequent actuation of the alternate key.

The above-type of mechanical arrangement suffers from several disadvantages. Even the simplest of such devices requires several moving parts which typically require intricate assembly operations. Such operations increase the cost of producing each switch assembly. Moreover, such devices are subject to ordinary mechanical wear with the attendant problems of frequent repair or replacement. In addition, bistable mechanical switching assemblies of the above-type exhibit many undesirable switching characteristics, e.g., contact bounce, which frequently result in the generation of spurious signals. Such assemblies are ill suited for use with many data processing devices, such as electronic calculators, which are highly sensitive to such spurious signals.

Magnetically operable switches are known which possess highly desirable switching characteristics. Magnetic reed switches, e.g., have found wide use in many switching applications because of their desirable switching characteristics, low failure rate, and low cost. A typical magnetic reed switch comprises a pair of reed contacts enclosed in a hermetically sealed envelope, usually glass. The contacts are so constructed and arranged within the envelope that the positioning of a magnet is proximity to the switch results in the actuation of that switch, usually by causing a pair of normally opened contacts to close; while removing the magnet from the vicinity of the switch causes the contacts to revert to their normally opened state.

SUMMARY OF THE INVENTION The invention disclosed herein comprises a bistable latching assembly having at least one magnetically operable switch. Adjacent the switch there is mounted a biasing magnet for providing a first magnetic field of insufficient strength to independently actuate the switch but of sufficient strength, once the switch is actuated, to hold the switch in that state. A LATCH magnet is movably mounted on a first key stem with magnetic poles oriented in a direction opposite the biasing magnet poles. A RELEASE magnet is movably mounted on a second key stem with magnetic poles oriented in generally the same direction as the biasing magnet poles.

Due to the field strength and orientation of the LATCH magnet, when this magnet is brought into proximity with the biasing magnet by actuation of the first key stem, the field associated with the biasing magnet is altered and concentrated in the vicinity of the switch sufficiently to actuate the switch. After removal of the LATCH magnet, the biasing magnet maintains the switch in this actuated state. When the RELEASE magnet is brought into proximity with the biasing magnet by actuation of the second key stem while the switch is in the actuated state, the field associated with the biasing magnet is diminished in the vicinity of the switch below that threshold magnitude required to maintain the switch in this state, and the switch returns to the quiescent configuration.

For a fuller understanding of the nature and advantages of the invention, reference should be had to the following ,detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. la-e illustrate the operation of the invention with one switch;

FIG. 2 is a perspective view partially broken away of a preferred embodiment utilizing a single switch; and

FIG. 3 illustrates the operation of the invention with two switches.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. la-e illustrate the operation of the invention.

A pair of electrically conductive spring blade contacts 12,14 constructed of a resilient magnetic material, e.g., nickel-iron alloy, are mounted in a normally open configuration so that electric current cannot flow between contacts 12,14. As will be apparent to those skilled in the art, the introduction of a magnetic field along contacts 12,14 results in a mutually attractive force therebetween which is opposed by the temper of these elements. As the magnetic field is gradually increased, this mutually attractive force also increases until it is sufficiently great to overcome the springlike mechanical resistance of contacts 12,14 to force the free ends thereof into overlapping contact. The magnitude of the magnetic field required to achieve this contact is termed the magnetic switching threshold of switch contacts 12,14. It will be appreciated that the magnitude of the magnetic field required to maintain contacts 12,14 in overlapping contact-termed the magnetic holding threshold-is less than the magnetic switching threshold. The actual value of these two parameters may be empirically determined for any given pair of contacts 12,14 by introducing a magnetic field along the contact pair, gradually increasing the value of this field until the contacts close, and subsequently gradually decreasing the magnetic field until the contacts open. While contacts 12,14 may preferably comprise the spring blade contacts of a magnetic reed switch, of the type described above, other suitable configurations will occur to those skilled in the art.

A biasing magnet 16 is positioned generally parallel to and spaced from contacts 12,14 so that a portion of the magnetic field associated with biasing magnet 16 lies along contacts 12,14 as shown in FIG. 1a. The proximity of biasing magnet 16 to contacts 12,14 is selected so that the magnitude of the mag netic field associated with biasing magnet 16 which lies along contacts 12,14 is insufficient to independently close contacts 12,14 but is sufficient to hold contacts 12,14 in an actuated (closed) configuration once they are actuated in the manner described below. Stated otherwise, the magnitude of the magnetic field in the immediate vicinity of contacts 12,14 provided by biasing magnet 16 lies in the range between the magnetic holding threshold and the magnetic switching threshold of contacts 12,14. The actual separation distance between biasing magnet 16 and contacts 12,14 required to provide a magnetic field in this range varies with several parameters, such as the strength of the magnet and the temper of the contacts. For any given case, it has been found most convenient to determine the optimum separation distance by experimentation.

FIG. 1b illustrates the manner in which the switch contacts 12,14 are actuated according to the invention. In this figure, a second magnet 17termed the LATCH magnetis illustrated as being positioned to the immediate right of biasing magnet 16 in field opposing relation thereto. The field opposing relation is obtained by positioning magnet 17 with the south magnetic pole thereof adjacent the south magnetic pole of biasing magnet 16. It is understood that, if the polarity of biasing magnet 16 were reversed from that illustrated, the same effect would be obtained by reversing the polarity of LATCH magnet 17 so that the north magnetic poles of the two magnets 16,17 would be adjacent. It is also understood that LATCH magnet 17 may bemoved into the position illustrated in FIG. 1b from any one of several initial positions, e.g., from an initial position to the right of that illustrated and in the same plane as the figure, or from an initial position coincident with that illustrated and in a plane above or below the plane of the figure.

As LATCH magnet 17 is moved into the FIG. 1b position, the increasing proximity of the opposing field associated with this magnet causes a distortion of the field associated with biasing magnet 16. Because of this distortion, the magnetic field associated with biasing magnet 16 is concentrated along contacts 12,14 to such an extent that the magnetic switching threshold of contacts 12,14 is exceeded and contacts 12,14 are closed. Once contacts 12,14 have been actuated, LATCH magnet 17 may then be removed from the vicinity of biasing magnet 16. Since the magnitude of the magnetic field from biasing magnet 16 along contacts 12,14 exceeds the magnetic holding threshold, however, these contacts thereafter remain in the actuated (closed) configuration. This is illustrated in FIG. 1a.

FIG. 1d illustrates the manner in which switch contacts 12,14 are deactuated according to the invention. In this figure, a third magnet 18termed the RELEASE magnet-is illustrated as being positioned to the immediate left of biasing magnet 16 in field assisting relation thereto. The field assisting relation is obtained by positioning magnet 18 with the south magnetic pole thereof adjacent the north magnetic pole of biasing magnet 16. It is understood that, if the polarity of biasing magnet 16 were reversed, the same effect would be obtained by reversing the polarity of RELEASE magnet 18 so that the north magnetic pole of this magnet would be adjacent the south magnetic pole of biasing magnet 16. It is also understood that RELEASE magnet 18 may be moved into the position illustrated in FIG. 1d from any one of several initial positions, e.g., from an initial position to the left of that illustrated and in the same plane as the figure, or from an initial position coincident with that illustrated and in a plane above or below the plane of the figure.

As RELEASE magnet 18 is moved into the FIG. 1d position, the increasing proximity of the assisting field associated with this magnet causes a distortion of the field associated with biasing magnet 16 which produces an opposite result from that described in conjunction with FIG. lb. More particularly, because of this distortion, the magnetic field associated with biasing magnet 16 is diluted or diminished along contacts 12,14 below the value of the magnetic holding threshold of contacts 12,14 permitting these contacts to open. Once contacts 12,14 have been thus deactuated, RELEASE magnet 18 may then be removed from the vicinity of biasing magnet 16. Since the magnitude of the magnetic field from biasing magnet 16 along contacts 12,14 lies below the magnetic switching threshold, however, these contacts thereafter remain in the deactuated (open) configuration. This is illustrated in FIG. 1e.

As will now be apparent, switch contacts 12,14 may be alternately actuated (closed) and deactuated (opened) by alternately positioning LATCH and RELEASE magnets 17,18 adjacent opposite ends of biasing magnet 16 in the manner described above. Further, it is notedthat a second successive positioning of the same magnet adjacent biasing magnet 16 will not alter the configuration of contacts 12,14. For example, with contacts 12,14 in the actuated configuration shown in FIG. 10, if LATCH magnet 17 is again placed in the position illustrated in FIG. lb, contacts 12,14 will remain actuated. Likewise, with contacts 12,14 in the deactuated configuration shown in FIG. 12, if RELEASE magnet 18 is again placed in the position illustrated in FIG. 1d, contacts 12,14 will remain deactuated.

It is noted that, for clarity, LATCH magnet 17 and RELEASE magnet 18 have each been illustrated in FIGS. 1b and Id, respectively, with their longitudinal axes substantially coincident with the longitudinal axis of biasing magnet 16. It is understood that such axial coincidence is not necessary, but merely illustrative, and that either one or both magnets 17,18

may be positioned with their longitudinal axes to either side of the axis of biasing magnet 16. Further, it has been found that it is not necessary to align the longitudinal axes of magnets 16, 17, and 18 in mutually parallel fashion, but that either one or both magnets 17,18 may be positioned with their longitudinal axes at a slight angle to the axis of biasing magnet 16.

FIG. 2 illustrates a preferred embodiment of the invention utilizing a single magnetically actuatable switch. A magnetic reed switch 21 of the type described above is mounted on a base plate 22 with the electrical end leads 23,24 engaged in a corresponding pair of holes in baseplate 22. Baseplate 22 may be constructed of any suitable nonmagnetic material, such as phenolic board. Leads 23,24 are electrically connected to associated circuitry (not shown) by any suitable means known to those skilled in the art.

A biasing magnet 26 is disposed on baseplate 22 generally parallel to and spaced from switch 21. The specific location of biasing magnet 26 is selected in accordance with the principles discussed above in conjunction with FIGS. la-e so that the magnitude of the magnetic field provided by biasing magnet 26 in the vicinity of switch 21 lies in the range between the magnetic switching threshold and the magnetic holding threshold of switch 21. Biasing magnet 26 may be permanently adhered to baseplate 22 by any suitable fastening means, such as gluing, potting, etc.

Baseplate 22 is provided with a pair of generally circular apertures for slidably receiving a pair of independently reciprocable similar key assemblies 30,31. Key assemblies 30,31 each comprise a key stem 32,33, a key top 34,35, and a bias return spring 36,37, respectively. Each key stem 32,33 comprises a cylindrical lower portion having an outer diameter sized to permit a comfortable sliding fit with the corresponding aperture in baseplate 22 and an upper portion with a square cross section having an outer dimension sized to permit a comfortable sliding fit with the corresponding aperture in a mounting plate 40. Mounting plate 40 and baseplate 22 are connected together to prevent relative motion therebetween by any suitable means known to those skilled in the art, such as cylindrical spacers.

Each key stem 32,33 is provided with a generally transverse circular groove for receiving a permanent magnet 42,44, respectively. It is understood that, although magnets 42,44 are illustrated as cylindrical, this preferred shape is not critical and magnets having a rectangular or square cross-sectional configuration are also suitable. To facilitate mounting of magnets 42,44, a generally transverse slot 46,47 is formed below the circular groove on key stems 32,33, respectively. If desired, magnets 42,44 may be cemented in their respective circular grooves, although this has not been found to be absolutely necessary.

Magnets 26, 42, and 44 are all oriented in accordance with the principles set forth above in the discussion of FIGS. la-e. Thus, if biasing magnet 26 is fastened to baseplate 22, with the north magnetic pole to the left and the south magnetic pole to the right as viewed in FIG. 2, magnet 42 is mounted on key stem 32 with the south magnetic pole to the left and the north magnetic pole to the right, while magnet 44 is mounted on key stem 33 with the north magnetic pole to the left and the south magnetic pole to the right. With this orientation, magnet 42 corresponds to the LATCH magnet and magnet 44 corresponds to the RELEASE magnet. If desired, the orientation of magnets 26,42 and 44 can all be reversed, so that magnet 44 corresponds to the LATCH magnet and magnet 42 corresponds to the RELEASE magnet.

In operation, depression of key top 34 moves LATCH magnet 42 into field opposing relation with biasing magnet 26 which results in actuation of magnetic reed switch 21 in the manner discussed above in conjunction with FIGS. Ia-e. When key top 34 is released, bias spring 36 returns key assembly 30 to the nonactuated position. Similarly, depression of key top 35 moves RELEASE magnet 44 into field assisting relation with biasing magnet 26, which results in deactuation of magnetic reed switch 21 in the manner discussed above.

When key top 35 is released, bias spring 37 returns key assembly 31 to the nonactuated position. In the preferred embodiment illustrated in FIG. 2, best results have been obtained by aligning key assemblies 30,31 with respect to magnetic reed switch 21 and biasing magnet 26 so that the path of motion of the longitudinal axes of LATCH magnet 42 and RELEASE magnet 44 lies in a vertical plane which cuts baseplate 22 in the region between the longitudinal axes of switch 21 and biasing magnet 26.

FIG. 3 illustrates a modification of the invention utilizing two magnetically operable switches. In this embodiment biasing magnet 16 is positioned approximately midway between two sets of spring blade contacts 12,14 and l2',14. Both sets of contacts possess substantially identical magnetic switching thresholds and magnetic holding thresholds. The proximity of contacts 12,14 and 12,14 to biasing magnet 16 is selected so that the magnitude of the magnetic field associated with biasing magnet 16 which lies along each set of contacts is insufficient to independently actuate either set but is sufficient to maintain both sets of contacts in an actuated configuration once they are actuated in the usual manner. Stated otherwise, the magnitude of the magnetic field in the immediate vicinity of contacts 12,14 and l2',14 provided by biasing magnet 16 is in the range between the magnetic holding threshold and the magnetic switching threshold of both sets of contacts.

A LATCH magnet 17 is movable into the field opposing position indicated by the broken outline. Likewise, a RELEASE magnet 18 is movable into the field assisting position indicated by the broken outline. Both LATCH magnet 17 and RELEASE magnet 18 function in a manner similar to that discussed above. Likewise, the magnetic polarity considerations described above also apply to the FIG. 3 embodiment. Due to the symmetry of the FIG. 3 arrangement, however, all magnets should be so positioned that their longitudinal axes lie in substantially the same vertical plane in order to ensure simultaneously actuation and deactuation of both sets of contacts.

In some applications, it may be desirable to actuate contacts 12,14 slightly before contacts l2',14' are actuated. Such serial actuation can be achieved byjudicious asymmetrical positioning of the two sets of contacts with respect to the longitudinal axis of biasing magnet 16, or by selecting a first set of contacts 12,14 with a lower magnetic switching threshold thaz. contacts 12',14' Other variations will occur to those skilled in the art.

While the foregoing provides a full disclosure of the preferred embodiments of the invention, it is understood that various modifications, alternate constructions, and equivalents may be employed without departing from the true spirit and scope of the invention. For example, other types of bias spring than that actually illustrated may be employed to provide a restoring force to each key assembly. Also key tops having other contours than those illustrated may be utilized in switch assemblies constructed according to the invention. Therefore, the above description and illustrations should not be construed as limiting the scope of the invention, which is solely defined by the appended claims.

What is claimed is:

1. A magnetically latched switch assembly comprising:

a magnetically operable switch having a magnetic switching threshold and a magnetic holding threshold less than said switching threshold;

a biasing magnet having a first pair of magnetic poles disposed adjacent said switch for providing a first constructed magnetic field in the immediate vicinity of said switch whose magnitude lies between said switching and said holding threshold;

a second magnet having a second pair of magnetic poles movable into field opposing relation with said biasing magnet for concentrating said first field in said immediate vicinity to a magnitude above said switching threshold to thereby actuate said switch; and

a third magnet having a third pair of magnetic poles movable into field assisting relation with said biasing magnet for diminishing said first field in said immediate vicinity to a magnitude below said holding threshold to thereby deactuate said switch.

2. The apparatus of claim 1 further including a baseplate for mounting said biasing magnet and said switch in spaced, substantially parallel relation.

3. The apparatus of claim 2 wherein said baseplate is cnstructed from a nonmagnetic material.

4. The apparatus of claim 2 further including first and second key assemblies mounted for reciprocal motion in a direction substantially normal to said baseplate;

each said assembly comprising a key stem having a transverse groove adapted to receive one of said second and third magnets;

a key top mounted on one end of said stem; and

bias means for biasing said key assembly toward a nonactuated position.

5. The apparatus of claim 4 wherein said baseplate is provided with a pair of apertures for guiding the lower portion of each of said key stems.

6. The apparatus of claim 4 further including a mounting plate disposed above said baseplate and provided with a pair of apertures adapted to slidably receive the upper portion of each of said key stems.

7. The apparatus of claim 6 wherein said bias means comprises a spring disposed between said key top and said mounting plate.

8. The apparatus of claim 4 wherein said second and third magnets are mounted in said switch assembly in axially aligned, spaced relation.

9. The apparatus of claim 4 wherein each of said second and third magnets is mounted for reciprocable motion of the longitudinal axis thereof in a plane substantially normal to said baseplate and lying between the longitudinal axes of said switch and said biasing magnet.

10. A magnetically latched switch assembly comprising:

first and second magnetically operable switches disposed in spaced, substantially parallel relation, each said switch having a magnetic switching threshold and a magnetic holding threshold less than said switching threshold;

a biasing magnet having a first pair of magnetic poles disposed between said switches for providing a first magnetic field in the immediate vicinity of each of said switches whose magnitude lies between said switching and said holding thresholds;

a second magnet having a second pair of magnetic poles movable into field opposing relation with said biasing magnet for concentrating said first field in said immediate vicinity to a magnitude above said switching thresholds to thereby actuate said switches; and

a third magnet having a third pair of magnetic poles movable into field assisting relation with said biasing magnet for diminishing said first field in said immediate vicinity to a magnitude below said holding thresholds to thereby deactuate said switches.

11. The apparatus of claim 10 wherein said first and second switches have substantially identical magnetic switching thresholds and substantially identical magnetic holding thresholds. 

1. A magnetically latched switch assembly comprising: a magnetically operable switch having a magnetic switching threshold and a magnetic holding threshold less than said switching threshold; a biasing magnet having a first pair of magnetic poles disposed adjacent said switch for providing a first constructed magnetic field in the immediate vicinity of said switch whose magnitude lies between said switching and said holding threshold; a second magnet having a second pair of magnetic poles movable into field opposing relation with said biasing magnet for concentrating said first field in said immediate vicinity to a magnitude above said switching threshold to thereby actuate said switch; and a third magnet having a third pair of magnetic poles movable into field assisting relation with said biasing magnet for diminishing said first field in said immediate vicinity to a magnitude below said holding threshold to thereby deactuate said switch.
 2. The apparatus of claim 1 further including a baseplate for mounting said biasing magnet and said switch in spaced, substantially parallel relation.
 3. The apparatus of claim 2 wherein said baseplate is c nstructed from a nonmagnetic material.
 4. The apparatus of claim 2 further including first and second key assemblies mounted for reciprocal motion in a direction substantially normal to said baseplate; each said assembly comprising a key stem having a transverse groove adapted to receive one of said second and third magnets; a key top mounted on one end of said stem; and bias means for biasing said key assembly toward a nonactuated position.
 5. The apparatus of claim 4 wherein said baseplate is provided with a pair of apertures for guiding the lower portion of each of said key stems.
 6. The apparatus of claim 4 further including a mounting plate disposed above said baseplate and provided with a pair of apertures adapted to slidably receive the upper portion of each of said key stems.
 7. The apparatus of claim 6 wherein said bias means comprises a spring disposed between said key top and said mounting plate.
 8. The apparatus of claim 4 wherein said second and third magnets are mounted in said switch assembly in axially aligned, spaced relation.
 9. The apparatus of claim 4 wherein each of said second and third magnets is mounted for reciprocable motion of the longitudinal axis thereof in a plane substantially normal to said baseplate and lying between the longitudinal axes of saiD switch and said biasing magnet.
 10. A magnetically latched switch assembly comprising: first and second magnetically operable switches disposed in spaced, substantially parallel relation, each said switch having a magnetic switching threshold and a magnetic holding threshold less than said switching threshold; a biasing magnet having a first pair of magnetic poles disposed between said switches for providing a first magnetic field in the immediate vicinity of each of said switches whose magnitude lies between said switching and said holding thresholds; a second magnet having a second pair of magnetic poles movable into field opposing relation with said biasing magnet for concentrating said first field in said immediate vicinity to a magnitude above said switching thresholds to thereby actuate said switches; and a third magnet having a third pair of magnetic poles movable into field assisting relation with said biasing magnet for diminishing said first field in said immediate vicinity to a magnitude below said holding thresholds to thereby deactuate said switches.
 11. The apparatus of claim 10 wherein said first and second switches have substantially identical magnetic switching thresholds and substantially identical magnetic holding thresholds. 